Fuel injection systems with which fuel injection into a combustion chamber of an internal combustion engine is performed have long been known. Injection systems of this kind comprise at least one injection valve (injector) and at least one control and regulating unit, connected to the injection valve, for controlling the injection process. Here, the injection valve has a space from which fuel can be injected into the combustion chamber through an injection opening. The opening and closing of the injection opening is performed by means of a closure element (nozzle needle), which can be actuated (moved) by an actuator. The space is supplied with fuel via a high-pressure reservoir and a fuel line.
The actuator is an element for moving the closure element. Thus, an injection process is controlled with the aid of the actuator. At the same time, the actuator is in direct drive connection with the closure element, which means that the actuator and the closure element are in direct mechanical contact or are connected to one another via interposed solid bodies, such as pins, levers or pistons. The essential point here is that there is no hydraulic or pneumatic coupling between the actuator and the closure element.
The actuator is a piezoelectric actuator which expands (increases in length) by virtue of the piezoelectric effect when supplied with electrical energy and in this way moves the closure element directly.
In fuel injection systems of this kind, it is necessary to detect the pressure prevailing in the pressure reservoir in order to be able to carry out appropriate control of the rail pressure. For this purpose, use is made in the prior art of special pressure sensors which are built into the pressure reservoir. This leads to an increase in overall system costs.